The present invention relates to a telephone system operating in time frames each consisting of a plurality of time slots and more particularly to a dial pulse register/sender.
The register/sender recognizes and generates supervisory signals such as on hook, off hook, and dial pulse to make connections in the telephone system.
In a pulse code modulated (PCM) digital switching system, a multiplicity of conversations are multiplexed serially along a two wire digitally multiplexed line commonly known as a T1 line. A plurality of T1 lines are multiplexed together into what is known as a line group. Each T1 line carries 24 PCM channels or time slots with a basic time frame of 125 microseconds. Each time slot is allocated 8 bits in which the sample conversation between a calling party and a called party is digitally represented in PCM format. One frame is equivalent to 125 microseconds and equals 1 frame bit plus 24 time slots of a T1 channel of 8 bits each of 193 bits per frame. The sample or frame rate is 8 kilohertz (the reciprocal of 125 microseconds). A typical frame structure includes 12 frames of 193 bits each. In a 12 frame format, the 8th bit of each time slot in frames 6 and 12 carries a signaling bit.
The signaling bits are used by the register/sender to detect the supervisory signals on hook, off hook, and dial pulse.
Heretofore, the number of register circuits required in a telephone system were based upon traffic distribution probabilities. If a large number of subscribers were to simultaneously require a register, some subscribers would not be able to complete the call because of physical limitations of the register.
Also, the prior art utilizes both on-hook and off-hook timers to digitally time changes of state of incoming signaling bits.
In accordance with the above described background, there is a need in a telephone system for an improved register/sender capable of detecting and generating supervisory signals such as on-hook, off-hook, and dial pulse for each time slot regardless of traffic distribution probabilities. It is desirable to avoid including both an on-hook and off-hook timer in the register, thereby resulting in less hardware.